Only a few days ago, the Cubs were expecting Marcus Stroman to come off the 15-day injured list and start against the White Sox Wednesday night. Now, not even president of baseball operations Jed Hoyer is sure when — and honestly, if — he’ll pitch for them again.

Imaging taken Monday revealed Stroman had suffered a right rib cage cartilage fracture, which the Cubs announced Wednesday before the Cubs’ 4-3 walk-off win. The 32-year-old hasn’t pitched since July 31, initially going on the IL with right hip inflammation. He’d thrown multiple bullpens during the team’s previous roadtrip, and even as recently as Sunday, the Cubs were confident Stroman would be ready to be activated to pitch in the series finale versus the White Sox.

But later that day, after he’d already thrown a lighter session in Toronto, Stroman reported discomfort on the right side of his ribs. That led to the MRI on Monday and the fracture diagnosis.

“It was really one where we had no idea what it was,” Hoyer said. “It’s not your usual pitching injury. It’s not an arm, it’s not a shoulder, it’s not an elbow. After the bullpen on Sunday, we assumed he was going to make the start [Wednesday]. So yeah, we were surprised.”

Neither Hoyer nor Cubs manager David Ross could provide clarity on how and when the injury occurred. They couldn’t provide a real timeline for his return. Stroman wasn’t available for comment.

Asked Wednesday if the injury could potentially end Stroman’s season, Hoyer said, “I have no idea. That’s the honest truth. We don’t really know at this point. I think we’ll obviously give him a real rest period and see how he feels. But I mean, again, it’s not a real common pitching injury. I’ve never seen that before.”

So, yes, with no clear return timeline at the moment, the Cubs will have to operate as they have the last couple of weeks without him. Javier Assad slotted into Stroman’s spot in the rotation Wednesday night, tossing his second straight quality start to keep the Cubs in the game.

While Stroman struggled prior to going on the IL (9.00 ERA in his last seven starts), the Cubs were able to play themselves back into the race. Even in the past two weeks, off-days in the schedule allowed them move the rotation around and mostly skip what would’ve been Stroman’s start days. But now that he’s out indefinitely, and with just one off-day between Friday and Sept. 13, they won’t have the ability to do so.

Drew Smyly and Hayden Wesneski are options currently on the major league roster to take the fifth-starter spot. Ross did say Wednesday he’s likely leaning to move Smyly back into the rotation (though he did pitch in relief in the ninth inning that night).

Stroman could return this season. With such an unusual pitching injury, and with 42 more games left in the regular season, the Cubs certainly can’t rule that out. Stroman will have to be symptom-free from the injury before he can pick up baseball activities, which will, of course, include a throwing program.

Until that happens though, the Cubs will have to continue their playoff push with him.

“We’ve been playing great baseball for quite a while,” Hoyer said. “I think this time of year, you just sort of kind of roll with things like that and move forward. We have depth. We’ve obviously been using that depth for a while and performing, so we have to keep doing that.

“I don’t know. I think at this time of year, you don’t stop and wallow too much. You say, ‘It’s too bad. We’d love to have him pitching for us,’ but he’s not, and we’ll keep playing well.”

More from Hoyer

• On his willingness to promote prospects if needed: “Look at 2019; we brought Nico [Hoerner] off his couch to play shortstop. So I mean, I think we’ve been creative when we feel like it’s the right thing to do for the organization. We’re not in that position right now. But certainly, when you have a chance to go to the playoffs and you have a chance to win, you’re a lot more aggressive with those kinds of decisions. When you’re not in the race or you’re building, I feel like it’s a lot easier to be clinical in those kinds of decisions than you would if you’re in the race.”
• On if No. 1 prospect Pete Crow-Armstrong’s skill set could find its way to the Cubs this season: “We’ll see. He’s been playing great. I mean, I think it’s way too early to talk about that. He hasn’t been in Triple-A too long. But he’s playing great, and it’s been fun to watch. Obviously, he has a skill set, certainly, that can benefit us in a lot of ways. But right now, we’re just focused on his development, and it’s been fun to watch.”
• On if rosters expanding to 28 players on Sept. 1 can provide some relief: “Not as much as it used to, though. That’s the challenge. It used to be, yes, I felt like before, you’d be grabbing as many guys as you could and you’d have a ton of guys up here and you felt like whatever fatigue you had in late August was going to go away once you could do that. But not really anymore. It’s kind of one pitcher and one hitter. So times have changed that way. It sort of makes you play basically straight up the rest of the way.”
• On if the current stretch factored into the trade deadline decision: “Certainly, we knew that our schedule wasn’t as hard as some teams’ schedules. I think that’s accurate. We played a lot of tough parts of our schedule in the first half of the year. So I think, just based on the math, the winning percentage of the teams we were playing was lower than the other contenders. You still have to win the games, you have to play the games, but yeah, it was nice to know that the hardest part of our schedule had passed us early in the year.”
• On the possibility of keeping Cody Bellinger around long term: “As good as it’s been for him, it’s been better for us. I mean, he’s been amazing. He’s sort of been like the centerpiece of this run we’ve had for the last 6-8 weeks. He’s been amazing. As I’ve said, he knows how we feel about him. We’d love to keep him here. He’s been a great fit for us, and he’s a great fit in the clubhouse for us. We’ll see.”